Traverse the matrix in spiral order and return the elements in traversal order.
Example 1
Input: matrix = [[1,2,3,4],[5,6,7,8],[9,10,11,12]]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]
Explanation: Spiral traversal of a rectangular matrix.
Output: [1,2,3,4,8,12,11,10,9,5,6,7]
Explanation: Spiral traversal of a rectangular matrix.
Example 2
Input: matrix = [[1,2,3],[4,5,6],[7,8,9]]
Output: [1,2,3,6,9,8,7,4,5]
Explanation: Elements are traversed in a spiral from the outer boundary toward the center.
Output: [1,2,3,6,9,8,7,4,5]
Explanation: Elements are traversed in a spiral from the outer boundary toward the center.